Effects of Surface Oxidation Treatments on the Interfacial Adhesion between Copper and Underfill

Delamination between the underfill and the copper pillar or copper solder pad is one of the major drawbacks of microelectronic packaging, leading to premature failure of the entire device. In this study, the chemical oxidation method was used to improve the adhesive strength between copper and underfill. It was found that the adhesive strength of copper and the underfill was significant increased by oxidation treatment of the copper. The wettability of the copper substrates was improved by the three oxidants (Na 2 S 2 O 8 , CuCl 2 , and KMnO 4 ) and was reduced by the oxidant of H 2 O 2 . SEM characterization results showed that different microstructures were formed on the oxidized copper surface. Through the analysis of the results of XPS, the surface layer of the oxidized copper changed from Cu metal layer to CuO layer. These results indicated that the wettability, microstructure, and oxide layer affected the adhesive strength of the copper/underfill interface.